This invention pertains to corrosion inhibitive pigments and more particularly to those derived from manganomanganic oxide.
The protection of metals with coatings is a complex phenomenon involving the restricted diffusion of water and oxygen to the substrate and the systems influence on surface passivity.
Thick coatings can reduce diffusion significantly but it has been pointed out that even the best systems do not completely prevent the permeation of both water and oxygen to a metal surface. It has also been shown that both the sodium and chloride ions diffuse through coatings providing that the concentration of the salt is at least 0.4 molar. Therefore, the cathodic reaction cannot be surpressed (1/2O.sub.2 +H.sub.2 O+2e.fwdarw.2OH.sup.-). In absence of corrosion inhibitive pigment, the corresponding anodic reaction will also take place (Fe.fwdarw.Fe.sup.++ +2e).
Chromium and lead based pigments have been effectively used in corrosion resistant coatings. Their toxicity, however, has resulted in their elimination from many paint formulations. It follows that this toxicity problem also extends to the use of chromium and lead compounds for metal corrosion inhibitors.
It is, therefore, an object of this invention to provide new corrosion inhibitive pigments.
Other objects will become apparent to those skilled in the art upon a reading of the specification.